Loops in Go

The basic loop in Go is written in standard C-like syntax:

for INITIAL; CONDITION; AFTER{
  // do something
}

INITIAL is run once at the beginning of the loop and can create variables within the scope of the loop.

CONDITION is checked before each iteration. If the condition doesn't pass then the loop breaks.

AFTER is run after each iteration.

For example:

for i := 0; i < 10; i++ {
  fmt.Println(i)
}
// Prints 0 through 9

Assignment

At Textio we have a dynamic formula for determining how much a batch of bulk messages costs to send. Complete the bulkSend() function.

It should return the total cost (as a float64) to send a batch of numMessages messages. Each message costs 1.0, plus an additional fee. The fee structure is:

• 1st message: 1.0 + 0.00

• 2nd message: 1.0 + 0.01

• 3rd message: 1.0 + 0.02

• 4th message: 1.0 + 0.03

• ...

Use a loop to calculate the total cost and return it.

Solution

package main

func bulkSend(numMessages int) float64 {
	total := 0.0

	for i := 0; i < numMessages; i++ {
		fee := 0.01 * float64(i)
		cost := 1.0 + fee
		total += cost
	}

	return total
}

1

Step 1

total := 0.0 — Start with zero total cost

2

Step 2

for i := 0; i < numMessages; i++ — Loop from 0 up to numMessages - 1

3

Step 3

fee := 0.01 * float64(i) — Fee grows each message (0.00, 0.01, 0.02, …)

4

Step 4

cost := 1.0 + fee — Each message costs $1 plus the fee

5

Step 5

total += cost — Add that cost to the running total

6

Step 6

return total — Return total cost after the loop

Example

func main() {
	println(bulkSend(3)) // Output: 3.03
	println(bulkSend(5)) // Output: 5.10
}

Summary for Obsidian Notes

Go for loop structure

for INITIAL; CONDITION; AFTER {
	// body
}

Example pattern

for i := 0; i < 10; i++ {
	fmt.Println(i)
}

Key ideas

• Use a variable (like total) to keep a running sum.

• Don’t return inside the loop unless you mean to stop early.

• Convert integers to floats when doing decimal math: float64(i).

Second Solution

How to increment fee properly

package main

func bulkSend(numMessages int) float64 {
	total := 0.0
	fee := 0.0

	for i := 0; i < numMessages; i++ {
		cost := 1.0 + fee
		total += cost
		fee += 0.01
	}

	return total
}

Explanation

Line	What it does
fee := 0.0	Start fee at zero
for i := 0; i < numMessages; i++	Loop once for each message
cost := 1.0 + fee	Base cost plus the current fee
total += cost	Add this cost to the total
fee += 0.01	Increase fee by 0.01 for next iteration

Example

func main() {
	println(bulkSend(3)) // Output: 3.03
	println(bulkSend(5)) // Output: 5.10
}

Each loop:

Message 1 → fee=0.00 → cost=1.00 Message 2 → fee=0.01 → cost=1.01 Message 3 → fee=0.02 → cost=1.02 Total = 3.03

Key Takeaway

Your logic was right — you just needed to:

• Initialize fee before the loop,

• Increment it inside the loop body (not in the for header).